The compounds of Formula I are described as 11,12-seco-prostaglandins because of their structural relationship to the naturally occurring prostaglandins.
The prostaglandins constitute a biologically prominent class of naturally occurring, highly functionalized C.sub.20 fatty acids; namely, 8,11,14-eicosatrienoic acid, 5,8,11,14-eicosatetraenoic acid and 5,8,11,14,17-eicosapentaenoic acid. Each known prostaglandin is a formal derivative of the parent compound, termed `prostanoic acid`; the latter is a C.sub.20 fatty acid covalently bridged between carbons 8 and 12 such as to form a trans, vicinally-substituted cyclopentane in which the carboxy-bearing side chain is `alpha` or below the plane of the ring and the other side chain is `beta` or above the plane of the ring as depicted in Formula III: ##STR4##
Within the last decade, prostaglandins have been shown to occur extensively in low concentrations in a myriad of mammalian tissues where they are both rapidly anabolized and catabolized and to exhibit a vast spectrum of pharmacological activities including prominent roles in (a) functional hyperemia, (b) the inflammatory response, (c) the central nervous system, (d) transport of water and electrolytes, and (e) regulation of cyclic AMP. Further details concerning the prostaglandins can be found in recent reviews of their chemistry [J. E. Pike, Fortschr. Chem. Org. Naturst., 28, 313 (1970)] and G. F. Bundy, A. Rep. in Med. Chem., 7, 157 (1972)], biochemistry [J. W. Hinman, A. Rev. Biochem., 41, 161 (1972)], pharmacology [J. R. Weeks, A. Rev. Pharm., 12, 317 (1972)], physiological significance [E. W. Horton, Physiol. Rev., 49, 122 (1969)] and general clinical application [J. W. Hinman, Postgrad. Med. J., 46, 562 (1970)].
The potential application of natural prostaglandins as medicinally useful therapeutic agents in various mammalian disease states is obvious but suffers from three formidable major disadvantages; namely, (a) prostaglandins are known to be rapidly metabolized in vivo in various mammalian tissues to a variety of metabolites which are devoid of the desired original biological activities, (b) the natural prostaglandins are inherently devoid of biological specificity which is requisite for a successful drug, and (c) although limited quantities of prostaglandins are presently produced by both chemical and biochemical processes, their production cost is extremely high; and, consequently, their availability is quite restricted.
Our interest has, therefore, been to synthesize novel compounds structurally related to the natural prostaglandins but with the following unique advantages: (a) simplicity of synthesis leading to low cost of production; (b) specificity of biological activity which may be either of a prostaglandin-mimicking or prostaglandin-antagonizing type; (c) enhanced metabolic stability. The combination of these advantages serves to provide effective, orally and parenterally active therapeutic agents for the treatment of certain human and animal diseases. Included are applications in the control of the immune response, blood clotting, and skin diseases such as psoriasis.
A number of publications describe the preparation of compounds said to be structurally related to prostaglandins. These publications include German Pat. No. 2,354,085 dated May 16, 1974 which describes certain substituted 11,12-secoprostaglandins which are said to have prostaglandin activity when orally administered. However, the present invention contemplates entirely different derivatives of 11,12-secoprostaglandins which have a different spectrum of biological activity as set forth hereinafter.
The compounds of the present invention are useful as pharmaceutically active compounds. Thus, these compounds are orally active in the treatment of conditions which are responsive to the actions of the natural prostaglandins. It is, of course, necessary to determine by routine laboratory testing which of the compounds of the present invention are most suitable for a specific end use. Some of the compounds of the invention have prostaglandin-like activity in that they mimic the effect of prostaglandin E.sub.1 in stimulating the formation of cyclic AMP in the mouse ovary in vitro. Certain of the compounds of the present invention raise the cyclic AMP levels in normal human skin (obtained from mastectomy), psoriatic plaques, and "normal adjuvant" skin tissue, all in an in vitro assay. Examples of the compounds which are particularly effective in this noted in vitro assay are:
Because of the response in the above-noted in vitro assay, these compounds are indicated as useful in the treatment of a variety of skin diseases including psoriasis, atopic dermatitis, non-specific dermatitis, forms of dermatitis due to irritation, allergic extrinsic dermatitis, scaly skin-cell carcinoma, lamella, ichthyosis, epidermolytic hyperketatosis, pre-malignant keratosis induced by sun, non-malignant keratosis, acne, and seborrheic dermatitis in humans, as well as atopic dermatitis and mange in domestic animals.
In addition, certain of the compounds of this invention are particularly effective in inhibiting the aggregation in platelets in blood stimulated with collagen to cause platelet aggregation; and thus, in inhibiting platelet aggregation, they are useful in preventing thrombus formation. Examples of these compounds are:
In addition, certain of the compounds of this invention are particularly effective in causing the release of growth hormone from pituitary glands in both in vivo and in vitro assays.
In a typical in vitro assay, rats are decapitated and the pituitary gland removed. The anterior pituitary gland is divided in two and one of the resulting hemipituitary sections is placed in a control bath of Kreb's Ringer bicarbonate buffer solution. The other hemipituitary gland section is placed in a similar buffer to which is added 2 ml. of the test solution of measured concentration of test compound. After a one-hour period, both the control bath and the test bath are analyzed for growth hormone production using a radioimmuno assay.
In an in vivo assay for measuring the stimulation of growth hormone production, male Holzmann rats are fasted overnight and anesthetized. Both the carotid artery and the jugular vein are canulated, thus providing access to the circulating blood entering and exiting the animal brain. A control blood sample is removed from the jugular vein prior to administration of the test compound. The test compound is then injected into the carotid artery and samples of the blood from the jugular vein taken at 10, 20, and 40 minutes following injection of the test compound. Both control samples and samples following administration of the test compound are analyzed for the presence of growth hormone by radioimmuno assay. Increase of growth hormone caused by the test compound is noted by reference to the amount of growth hormone in the control sample. Compounds found to be active in these tests are useful in stimulating growth hormone in poorly-functioning pituitary glands.
An example of a compound which is active in each of the in vitro and in vivo tests above is 8-methylsulfonyl-12-hydroxyheptadecanoic acid.
The compounds of this invention are also indicated to be useful in therapy as regulators of the immune response. The basis for their activity in this area is their ability to stimulate cyclic-AMP formation in cells. Agents, including the E prostaglandins, that increase cellular cyclic-AMP concentration, interfere with the cell-mediated immune response by inhibiting lymphocyte expression in response to antigen, by inhibiting release of pathological mediators from sensitized lymphocytes, and by inhibiting the killing of target cells by such lymphocytes. Various assays which depend upon the measurement of some function of the immunologically competent lymphocyte can be used to demonstrate that the prostaglandin analogs of this invention are similarly active. For example, the release of lymphokines (proteins that are agents of inflammation and tissue destruction) from sensitized lymphocytes in culture is strongly inhibited by these analogs in low concentrations. Thus, it is apparent that the compounds of this invention are applicable to the treatment of those autoimmune diseases in whose pathogenesis a cell-mediated immune reaction is involved. Such diseases range from contact dermatitis to such chronic destructive diseases as rheumatoid arthritis and possibly multiple sclerosis and systemic lupus erythematosus.
The present prostaglandin analogs are also effective in preventing the rejection of transplanted organs. The biochemical basis for this action is the same as outlined in the preceding paragraph, for the rejection of organ grafts is considered to be predominantly a cell-mediated immune phenomenon and the hallmark of organ rejection is the infiltration of cytotoxic lymphocytes into the graft. Direct evidence that the compounds of this invention can retard or prevent transplant rejection has been obtained in the rat renal allograft model; in this system, administration of the compounds of the present invention prevents the rejection of the transplanted kidney and the subsequent death of the host rat, which events invariably occur in the cases of untreated rats or those treated with the immunosuppressants.
An example of a compound which is an effective regulator of the immune responses of the types described above is 8-methylsulfonyl-12-hydroxyheptadecanoic acid.
Because of their biological activity and ready accessibility, the compounds of the invention are also useful in that they permit large scale animal testing useful and necessary to understanding of these various disease conditions such as dwarfism caused by poorly-functioning pituitary glands, stroke (thrombus formation), skin diseases such as psoriasis, and the like. It will be appreciated that not all of the compounds of this invention have these biological activities to the same degree but the choice of any particular ones for any given purpose will depend upon several factors including the disease state to be treated.
The compounds of this invention can be administered either topically or systemically (i.e., intravenously, subcutaneously, intramuscularly, orally, rectally, or by aerosolization in the form of sterile implants for long action).
The pharmaceutical compositions can be sterile injectable suspensions or solutions, or solid orally administrable pharmaceutically acceptable tablets or capsules; the compositions can also be intended for sublingual administration, or for suppository use. It is especially advantageous to formulate compositions in dosage unit forms for ease and economy of administration and uniformity of dosage. `Dosage unit form` as a term used herein refers to physically discrete units suitable as unitary dosages for animal and human subjects, each unit containing a predetermined quantity of active material calculated to produce the desired biological effect in association with the required pharmaceutical means.
Illustratively, a sterile injectable composition can be in the form of aqueous or oleagenous suspensions or solutions.
The sterile injectable composition can be an aqueous or oleagenous suspension or solution. Suspensions can be formulated according to the known art using suitable dispersing and wetting agents and suspending agents. Solutions are similarly prepared from the salt form of the compound. For the laboratory animals, we prefer to use incomplete Freund's adjuvant or sterile saline (9%) as carrier. For human parenteral use, such as intramuscularly, intravenously, or by regional perfusion, the diluent can be a sterile aqueous vehicle containing a preservative; for example, methylparaben, propylparaben, phenol, and chlorobutanol. The aqueous vehicle can also contain sodium chloride, preferably in an amount to be isotonic; as well as a suspending agent, for example, gum arabic, polyvinyl pyrrolidone, methyl cellulose, acetylated monoglyceride (available commercially as Myvacet from Distillation Products Industry, a division of Eastman Kodak Company), monomethyl glyceride, dimethyl glyceride or a moderately high molecular weight polysorbitan (commercially available under the tradenames Tween or Span from Atlas Powder Company, Wilmington, Delaware). Other materials employed in the preparation of chemotherapeutic compositions containing the compound may include glutathione, 1,2-propanediol, glycerol and glucose. Additionally, the pH of the composition is adjusted by use of an aqueous solution such as tris(hydroxymethyl)-aminomethane (tris buffer).
Oily pharmaceutical carriers can also be used, since they dissolve the compound and permit high doses. Many oily carriers are commonly employed in pharmaceutical use, such as, for example, mineral oil, lard, cottonseed oil, peanut oil, sesame oil, or the like.
It is preferred to prepare the compositions, whether aqueous or oils, in a concentration in the range of from 2-50 mg./ml. Lower concentrations require needless quantities of liquid. Higher concentrations than 50 mg./ml. are difficult to maintain and are preferably avoided.
Oral administration forms of the drug can also be prepared for laboratory animals or human patients provided that they are encapsulated for delivery in the gut. The drug is subject to enzymatic breakdown in the acid environment of the stomach. The same dosage levels can be used as for injectable forms; however, even higher levels can be used to compensate for biodegradation in the transport. Generally, a solid unit dosage form can be prepared containing from 0.5 mg. to 25 mg. active ingredient.
Whatever the mode of administration, doses in the range of about 0.10 to 20 milligrams per kilogram of body weight administered one to four times per day are used, the exact dose depending on the age, weight, and condition of the patient, and the frequency and route of administration.
The low cost and ready accessibility of the compounds of this invention make them particularly promising for applications in veterinary medicine in which field their utilities are comparable to those in human medicine.